Transdermal drug delivery systems are known and have achieved generally widespread acceptance in providing systemic therapy for certain human conditions. (As used herein the term "drug" is intended to be interpreted in its broadest sense to include any material that is to be delivered into the body to provide a desired, usually beneficial, effect.) Typically, these transdermal drug delivery systems are diffusional in nature and their applications have been somewhat limited in that the rate of administration of drug to the skin designed into the delivery systems must be restrained (controlled) to take into account the skin's permeability to the drug and therapeutic plasma level, and the marked intra and inter-individual differences in skin permeability. That is to say, these system's rate-limiting resistance to drug transport must be selected to be considerably higher than the resistance of the skin to drug absorption for controlled, systemic therapy. Conversely stated, to control the rate of drug absorption from diffusional dosage form designs the flux of drug from the system must be considerably lower than the limiting absorption flux of the skin.
Among such diffusional dosage systems, or bandages for the transdermal administration of drugs are those described in U.S. Pat. Nos. 3,797,494 and 4,031,894, which collectively disclose bandages in the form of laminates including a backing, a drug reservoir, a microporous membrane and a contact adhesive layer. The microporous membrane in such devices acts to limit the rate of drug administration.
Osmotic systems useful in the topical administration of drugs are also known. Perhaps the systems which are most relevant to this invention are those shown in U.S. Pat. Nos. 4,014,334 and 4,077,407, each of which discloses an osmotic device in which an active agent, or drug, is contained within a compartment defined by a wall formed from a material permeable to an external fluid but impermable to the active agent contained within the compartment. An aperture in the wall communicates with the chamber to permit dispensing of the active agent which exhibits an osmotic pressure gradient across the wall against the external fluid, or which is mixed with an agent exhibiting such pressure gradient when used for the topical application of ARC 695 systems do not achieve the relatively high transdermal delivery rates envisioned through use of the present invention.